Abstract
Future HVDC power transmission systems faults may lead to transient overvoltages of types not covered by present HVDC cable type tests. Among these are the so-called Temporary
Overvoltages (TOVs), characterized by a very slow front and long tail transient superimposed on a dc voltage. To clarify to what extent HVDC cable grade XLPE insulation withstands such TOVs, the maximum withstand field of 0.3- and 0.5-mm thick samples was determined during TOVs of different front and decay times. The 234 samples tested included samples with small contamination particles inserted to emulate defects in the insulation. The samples without particles showed an impressive dielectric strength, up to 600 kV/mm. The samples with contamination particles suffered breakdowns at considerably lower fields, most of them in the range 250–350 kV/mm. More important, no substantial differences in dielectric strength were observed between the different TOVs, even though the front time ranged from 0.25 ms (as in a standard switching impulse) to 10 ms.